Two speckle patterns produced from the same rough surface by two different illuminations are correlated. The correlation depends on the surface roughness. The two illuminations were obtained here by varying the angle of incidence of a coherent plane wave on the surface. The speckle patterns are recorded on the same film by double exposure. By placing this film in a convergent laser beam, Young fringes are observed in the Fourier plane. The correlation of the speckle patterns is obtained by measuring the visibility of the fringes. The theoretical calculations have been performed for a normally distributed surface. The experimental results are in good agreement with theory.

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Time-lapse imaging of biological samples is important for understanding complex (patho)physiological processes. A growing number of point-of-care biomedical assays rely on real-time imaging of flowing or migrating cells. However, the cost and complexity of integrating experimental models simulating physiologically relevant microenvironments with bulky imaging systems that offer sufficient spatiotemporal resolution limit the use of time-lapse assays in research and clinical settings. This paper introduces a compact and affordable lens-free imaging (LFI) device based on the principle of coherent in-line, digital holography for time-lapse cell migration assays. The LFI device combines single-cell resolution (1.2 μm) with a large field of view (6.4 × 4.6 mm2), thus rendering it ideal for high-throughput applications and removing the need for expensive and bulky programmable motorized stages. The set-up is so compact that it can be housed in a standard cell culture incubator, thereby avoiding custom-built stage top incubators. LFI is thoroughly benchmarked against conventional live-cell phase contrast microscopy for random cell motility on two-dimensional (2D) surfaces and confined migration on 1D-microprinted lines and in microchannels using breast adenocarcinoma cells. The quality of the results obtained by the two imaging systems is comparable, and they reveal that cells migrate more efficiently upon increasing confinement. Interestingly, assays of confined migration more readily distinguish the migratory potential of metastatic MDA-MB-231 cells from non-metastatic MCF7 cells relative to traditional 2D migration assays. Altogether, this single-cell migration study establishes LFI as an elegant and useful tool for live-cell imaging.

An increasing number of in vivo and in vitro neuro-engineering applications are making use of colloidal particles as neuronal cell carriers. Recent studies highlight the shortcomings of commercial glass particles and stress the benefit of using soft microgel particles (MGPs) instead. This study describes first the fabrication of MGPs from telechelic poly(2-methyl-2-oxazoline)s (PMeOx) cross-linkers and hydrophilic neutral (hydroxyethyl)methacrylate (HEMA) or charged 2-methacryloxyethyltrimethylammonium (METAC) monomers by emulsion polymerization, and it discusses their ability to support cell growth. It establishes that uncharged copolymers lead to MGPs with nonfouling properties inappropriate for cell culture, and it provides a protocol to amend their surface properties to enable cell adhesion. Finally, it demonstrates that the introduction of positive charges by METAC is necessary to obtain surface properties suitable for neuronal cell development. Through the optimization of the PMeOx30 MGP properties, this work provides general guidelines to evaluate and tune MGP chemistry to obtain microcarriers for neuro-engineering applications.

The need for sensitive imaging techniques to detect tumor cells is an important issue in cancer diagnosis and therapy. Surface-enhanced Raman scattering (SERS), realized by chemisorption of compounds suitable for Raman spectroscopy onto gold nanoparticles, is a new method for detecting a tumor. As a proof of concept, we studied the use of biocompatible gold nanostars as sensitive SERS contrast agents targeting an ovarian cancer cell line (SKOV3). Due to a high intracellular uptake of gold nanostars after 6 hours of exposure, they could be detected and located with SERS. Using these nanostars for passive targeting after systemic injection in a xenograft mouse model, a detectable signal was measured in the tumor and liver in vivo. These signals were confirmed by ex vivo SERS measurements and darkfield microscopy. In this study, we established SERS nanostars as a highly sensitive contrast agent for tumor detection, which opens the potential for their use as a theranostic agent against cancer.